1. Field of the Invention
The present invention is directed to a system and method for producing partitioned tubular film cartridges, and, more particularly, to a system and method for producing mine roof bolt resin cartridges that can be used to anchor bolts and other supports in mine roofs.
2. Description of Related Art
Mine roof bolts and other structural elements are often anchored into rock, concrete or the like, by a combination of adhesives and mechanical structures such as an expansion anchor at the distal end of the bolt. Bolts sized ⅝ inch to 1¼ inch in diameter are used in boreholes varying from ¾ inch to 2 inches in diameter. Adhesives are generally formed in place within the borehole by providing a resin cartridge that includes two compartments, with a polymerizable (curable) resin component in one compartment, and a hardener or catalyst component in another compartment. A borehole is drilled in the rock, and the cartridge containing the polymerizable resin and catalyst is inserted into the blind end of the borehole. When a mine roof bolt is inserted into the borehole, the distal end of the bolt ruptures the package so that the resin and catalyst components are mixed. Upon insertion of a bolt into a borehole, the bolt is rotated to shred the package and enhance mixing until the resin hardens to a degree that nearly prevents the bolt from being rotated, and the mixed composition is allowed to cure.
The most common types of resin cartridges are known as two component systems because they contain a catalyst and a resin. These two component resin cartridges are produced via a variety of techniques. In general, these techniques involve advancing a web of a film into a tube shape having a divider within the tube, thereby producing a partitioned tube. One compartment of the partitioned tube receives the resin component and the other compartment of the partitioned tube receives the catalyst component. The tube is sealed off at intervals to produce lengths of the filled package. The partitioned package is filled in a packaging machine that receives a stream of a curable resin into one compartment and a stream of catalyst in the other compartment. The resin and the catalyst are prepared in separate mixing vessels and are transferred to the packaging machine. The preparation and transfer of the resin and the catalyst has conventionally been conducted in batch operations or semi-continuous operations with minimal feedback or process controls. U.S. Pat. No. 3,889,446 (Simmons et al.) provides an example of such a process.
Another type of resin cartridge, known as a two-speed resin cartridge, contains, for example, in a first compartment, both a fast and a slow setting resin and, in a second compartment, a catalyst. As used herein, a “fast setting resin” is a resin that has a short time to set up or “gel” when in contact with a catalyst. Equivalently, a “slow setting resin” is a resin that has a long setting time. Typically, the faster setting resin will also have a faster cure time, where the cure time is the time it takes for the resin to achieve full adhesive strength. The setting time of a resin is usually affected by the chemical make up of the resin and the catalyst components.
Like with the two-component resin system described above, the fast and slow setting resins are separated from the catalyst in the cartridge so that a reaction is prevented prior to rupturing the barrier dividing the compartments. The use of two resins of distinct setting speeds permits bolt-pretensioning. The faster setting resin is disposed toward one end of the cartridge while the slower setting resin is disposed toward the other end of the cartridge. The two-speed cartridge is typically inserted into the borehole so that the end containing the faster resin abuts the top of the borehole allowing a bolt inserted into the borehole to be anchored by the resin at the top of the hole first. Orienting the cartridge in such a way, with the faster end inserted first, is important to the success of the anchoring medium to provide support. For instance, once the bolt has been anchored at the top of the borehole, a nut may be tightened at the opposite end of the bolt to apply a compressive force to an associated support plate abutting the mine roof surface to help compress and support the mine roof. After the nut has been sufficiently applied, the slower setting resin disposed toward the other end of the bolt can fully solidify to anchor the remaining portion of the bolt in the borehole.
Currently, two-speed resin cartridges, while known, are not widely available in the United States primarily due to the manufacturing difficulties and costs associated with their manufacture. Typically, a faster setting and slower setting resin are pumped from individual tanks to a resin cartridge packaging machine through individual feed pipes, each of which is associated with a pump and a valve at the end near the packaging machine. The operator then alternately selects from the resins in the feed pipes for injection into a cartridge to create a two-speed resin cartridge. However, the resins and catalysts used in roof bolt operations are highly viscous and flow through piping in a laminar fashion. These properties make it difficult to cleanly and quickly transition from one resin to another during the cartridge filling process. In some instances, four to ten times the amount of resin that is contained in the pipes and pumps of a cartridge filling system is lost as waste while making these transitions. Typical resin transition lengths within the cartridge can run up to 200 mm or more, while it is desirable to keep the transition lengths around 25 mm so that most of the bolt is in tension during setting. Moreover, the individual pumps must be started and stopped when changing between the different resins, which uses a great deal of energy and puts elevated strain on the valves that hold back the mass of material in the feed pipes. In addition, using multiple single-resin, two component system layouts to produce cartridges having multiple setting times requires a separate mixing and piping system for each resin time. Multiplying the number of pumps and piping running to the packaging machine exponentially increases the complexity of the overall production system and further increases waste.